Study On Power System Restoration Schemes With The Aid Of High-voltage Direct Current Transmission

LCC-HVDC has the advantages of large transmission capacity,fast start-up and adjustment and flexible control,it has been rapidly developed both at home and abroad in recent years.It can be incorporated into the design of the system restoration schemes and effectively make up for the shortcomings in the past power system restoration schemes.The positive role it plays in improving the existing restoration control strategy and further optimizing the restoration control effect can not be ignored.Therefore,it is urgent to carry out in-depth research on the system restoration schemes with the aid of LCC-HVDC.First of all,this paper points out the control method and DC starting current value which should be adopted in the starting process of LCC-HVDC channel through theoretical analysis and operation experience,then a starting model of LCC-HVDC is set up in PSCAD/EMTDC platform,from the perspective of reducing the frequency deviation and voltage fluctuation of AC system,the DC voltage required for DC start-up is determined through simulation verification and result analysis.The existing power system restoration schemes with the aid of LCC-HVDC ignore the relationship between the DC transmission power and the strength of the AC power system as well as the influence of grid reconfiguration and load input on the AC power system on the post DC power boost,in view of which a black-start scheme of power system with DC terminal location considering aftereffects is considered.The optimization goals are as follows: the total generation output in the early stage is as much as possible,the system operation is as safe and reliable as possible when the DC power is increased and the feasibility of DC power greatly rapid increase is as high as possible in the late stage,the mixed particle swarm optimization algorithm and Dijkstra algorithm are combined to solve the Pareto optimal solution set,then the Pareto optimal solution is sorted by the modified technique for order preference by similarity to ideal solution to determine the most satisfactory restoration scheme.Considering the frequency regulation characteristics,power factor,capacity size and position of the restored load on the end system security when LCC-HVDC makes its access,combined with the operation characteristics of load input during the system restoration process,a method for load restoration optimization considering the influence of LCC-HVDC access on the system security is proposed.The optimization goals are designed to minimize the frequency deviation,minimize the voltage offset of the nodes and maximize the power flow entropy of the receiving grid,NSGA-II algorithm is used to solve the Pareto optimal solution set of load restoration,based on which the most satisfactory solution is selected by the gray relational analysis model.